Trunk and attendant&#39;s circuit arrangement for an electronic switching exchange



lIuly 27, 1965 Filed Nov. 28, 1961 D. K. MELVIN TRUNK AND ATTENDANTS CIRCUIT ARRANGEMENT FOR AN ELECTRONIC SWITCHING EXCHANGE 2 Sheets-Sheet 1 DONALD K. MELVIN ATTY.

July 27, 1965 D. K. MELvlN 3,197,569

TRUNK AND ATTENDANT'S CIRCUIT ARRANGEMENT FOR AN ELECTRONIC SWITCHING EXCHANGE Filed Nov. 28, 1961 2 Sheets-Sheet 2 To CENTRAL coNF. OFFICE MUU RINGING DETECTOR NORMAL- DIAL OUT-CONF.

CLOSURE SWITCH MULTIPLEX GATE | l IN VEN TOR. j DONALD K. MELvaN ATTY,

United States Patent O mense@ Aun attenuante chacun anastaciaarr mnemonic swrrcnnso rThis invention relates to a trunk and attendants circuit arrangement for an electronic switching exchange, and more particularly to a ringdown trunk circuit arrangement for use in a private automatic branch erchange having time division multiplex scanning and supervisory control.

The object of the invention is to provide an eiiicient and effective arrangement for the handling of calls between local subscribers and central ofce trunk lines.

A principal feature of the invention relates to an arrangement for detecting ringing current signals received over the trunk line on an incoming call to repeat a seizure signal to the local switching equipment upon the first splash of ringing current and to give an indication of the call, such as a flashing lamp signal, which continues until the attendant operates the answer key.

Another feature relates to a common attendants dialing circuit which is associated only with the trunk circuit having the answer key in the answer position, arranged so that the attendant may dial a call into the local exchange or alternatively dial out over the trunk line, but never both simultan-euosly, under the control ot a di l-contrcl key in each trunk circuit.

ilurther features relate to lia-Shing recall, and to a common release circuit.

The above-mentioned and other objects and features or this invention and the manner of obtaining them will become more apparent and the invention itself will be 'nest understood by reference to the following description ot an embodiment of the invention taken in conjunction with the accompanying drawings comprising FlGURES 1 and 2, wherein:

F G. 1 is a single line block diagram of a time division ritmi-ei: telephone exchange; and

MG. 2 is a functional block and schematic diagram oi one trunk circuit and part of the attendants equipment.

The electronic exchange is shown by a single line block diacram in lili?. l. Line circuits LCli to LGSS associated with stations Sli to Si are connected in cornmcn to the end Mil of a time division multiplex transmission highway. Link circuits Ll to Llld and trunk l l to are connected in common to the lr/ILZ oi the transmission highway. .Equipment nd an attendants telephone ld are common to the trunk circuits Tii to Tll.

A tran lesion control unit il@ may ne interposed between the two ends oi the multiplex transmission highway. Any two line circuits may be connected through ml: circuit, or any line circuit may be connected to y trunk circuit by selectively supplying control pulses to them.

The signalling circuits 1 7@ supply supervisory tones and ring control signals which are transmitted either by time division multiplex over line T72 and the highway Miei-ML2, or over conductors in line lSS-l.

The function of remembering which circuits are interconnected on a time division multi alex basis over highway hill-ML2 and of supplying control pulses to the selected transmission gates in the appropriate time slots is performed by a liiUh-speed memory and logic llSll.

Ill

ICC

The control pulses are supplied to the line circuits over line 132-134, to the link and trunk circuits over line lll?, and to the signalling circuits over line 62.

The selective registration in the high-speed memory is controlled by the low-speed memory and logic Mill. These circuits Mtl control the line-iinding function ot scanning to find a line which has initiated a call and causing a connection to be established to the calling line; and the connector function of detecting dial pulses from the calling line and causing a connection to be established to the called line, and also trunk and transfer functions. These control circuits Mii are shared by all of the links and trunks on a time division basis, using a low-speed ferrite core memory for storage.

The pulse sources in@ comprise pulse generators and distributors for supplying all of the pulses required by the exchange.

A private automatic branch exchange of the type shown in FG. l is disclosed in the United States patent application of A. H. Faulkner and D. K. Melvin for an Electronic Switching System, Serial No. 135,823, tiled September 5, 1951. FIG. 3 of that patent application shows a simple functional block diagram of a trunk circuit. This trunk circuit and equipment 195' common to all of the trunks is shown in further detail in FIG. 2 of the present application.

Referring now to FlG. 2, each of the trunk circuits such as trunk TKll includes a three-position answer key 1376i, a dialing and conference key 138i?, a busy lamp i360, and a ring lamp 1353i? which appear on a cordless attendants cabinet. The cabinet will also have a common dial lamp i326 shown in the common equipment wil. The line loop from the central otce is connected through normally closed contacts on the right-hand side of switch 137'@ to the line i331 and thence through a diode bridge l3tl3, a loop-closure switch i336, and a line transformer i352, to a multiplex gate TGfl. The multiplex gate TG@ causes communication signals associated with the trunk Thil to be transmitted to and received from the two-way time division multiplex common transmission conductor ML2 in the individual time slot under the control o a pulse on conductor BP2?. The gate TK@ is selectively controlled by a switch-through signal appearing in its time slot DP29 on conductor 921. The various liip-iiops and logic circuits control the loop closure, and other functions in the trunk circuit. The logical true or l condition is -5 volts, and the false or "0 condition is ground potential.

The operators telephone lrlli is connected over a line including its own loop-closure switch i331 and a diode bridge circuit to the contacts of the answer keys of all trunks. Any answer key in the center answer position connects the operators telephone loop to the corresponding central office trunk loop. The operators dial llllt is isolated from her telephone circuit 1Std, and is used to control either the loop closure switch i331 for outgoing dialing to the central oice, or to dial in through the monostable vibrator i312 and line i3d@ through circuits or" one of the trunk circuits to set up a connection through the electronic exchange.

The loop-closure switches 't and 153i may comprise electronic arrangements such as transistor circuits.

The exchange is also provided with a conference circuit CF which is connected in multiple to the keys 138@ of all of the trunk circuits. This conference multiple CF may also be reached through special line circuits to permit connections from local subscribers.

A common release key i325 is supplied with time slot identiiication pulses from all trunks, through contacts of the respective answer keys and gate 1324. When the key. i325 is depressed the Dl pulse from any trunk having its key li in answer position is supplied in coincidence normal.

vmally 45 volts,"and becomes a'steady ground potential when a train of pulses appear on lead Rt incoincidence with the pulses on lead DP29, during the ringing sequence state in common control for this trunk.

Assume now that an incoming call is received from the central office. Ringing current applied to the central oice loop is applied through the right-hand contacts of key 1370 to line 1301 and appears at the input of ringing detector 134,0. The ringing detector equipment 1340 converts the alternating ringing current to a negative fivevolt signal to set the ip-liop Rd. The nip-flop Rd in its set l state applies a signal through gate 1351 under the control of the- 120 IPM interrupter signal to amplifier 1352 to flash the ring lamp 1350. The output from 'flipop Rd is also applied through gate 1342 to an input of gate 336, so that in the time slot DP29 pulses appear on the common trunk supervisory conductor E2. Sinceflip-v op Rd will not be reset until the operator answers this trunk, the ringing lamp will continue to ash even after ringing current has ceased to be applied to the trunk. The purpose of marking lead E2 in this trunks time slot, at this time, is to make sure that the electronic trunk circuit will be available at the time when the operator wants to dial the local subscriber number into this trunk. If this trunk had not been marked busy at this time it would be possible for a subscriber on the electronic exvchange to place an outward call and seize the trunk before the operator was able to extend the incoming call to the electronic exchange over it. It should be noted that the answer key 1370 in the trunk circuit is a three-position key with an offset cam. The normal position of this key prevents the operators telephone circuit from bridging a trunk circuit. To answer an incoming call .the operator operates the answer key 1370 to the answer position thus tripping the ring trip relay of the central office electromechanical exchange and, at the same time, resetting flip-flop Rd.V The reset signal is applied from common conductor 1316 through contacts on the left hand side of key 1380 and contacts on the left hand side of key 1370 to lead .1317, and thence through an emittervfollower amplier 1344 to the reset input of the ilip-flop Rd. '(It is assumed that the key 1380 is inrits normal position, that is operated to the left.) Even though flip-liep Rd has been reset, this trunks time slot will be marked busy on lead E2 by the signal applied through the answer key 1370 to conductor 1317 which is applied through gate 1342 to the input of gate 336.

When flip-flop Rd was reset, the flashing ring lamp 1350 was extinguished. The operator may now obtain the name or number of the desired party from the calling party. In order to enable the operator to dial the desired number without having to operate any more keys, and without having a local dial tonego out over the trunk, it is necessary to provide a common dial lamp 1320 on the attendants cabinet to signal the attendant when dialing may proceed.V At any given time the common dial lamp 1320 is associated with the one answer key that is off mechanical trunk While dialing into the electronic trunk, this Vmay be done by operating the answerV key to the hold position. VHolding the electro-mechanical trunk will not affect dialing or transmission over the electronic trunk. The common dial lamp 1320 receives its input through an amplifier 1321 from gate 1322. The signal through key 1325 is normally true, and when dialing into the electronic exchange may commence, a signal appears on lead Dt in coincidence with signal P2 to enable the gate 1322 and thus causethe lamp 1320 to light. Y

The operators dial circuit is equipped with a standard telephone dial 1311 and a monostable multivibrator 1312. When the dial impulse springs are closed, a signal of 5 volts will be present on the make output to lead 1316 from the multivibrator. When the impulse springs are If the attendant desires to hold the electro-V l open, a signal of -5 volts will be present on the break lead to an input of gate 1314. impulses on the make lead are used for dialing the electronic trunk while impulses on the break lead are used for pulsing the trunk loop. When the attendant desires to dial the electronic Vtrunk circuit the dial-out key must be in its normal position. Dial impulses on the make lead 1316 of the multivibrator are applied through contacts of key 1380 and key 1370 Vto lead 1317 and thence through gate 1342 to gate 336; Therefore the dial impulses will appear as a train of pulses in time slot BP2@ on lead E2. This train of pulses appears when the dial impulse springs of dial 1311 are closed and will not be present when the impulse springs are open. A connection is then set up in the electronic exchange as explained in the said copending application so that the trunkTK1 and the selected local subscriber line are connected by way of a time division multiplex path occurring in time slot DP29 on the common multiplex conductor. A signal condition is also returned over line from the common control equipment,4A which by way of the loop closure logic 350 sets the flip-flop Et. This operates the loop closure switch 1330 to its operative position to complete the transmission path, applies a signal through gate 1342 to supply an input to gate 336 so that pulses continue to appear during time slot DP29 on conductor E2, and applies a signal through gate 1363 and amplifier 1364 to light the busy lamp 1360. The attendant retires from the circuit by returning the answer key 1380 to its normal position. VThe busy lamp 1360 will burn steadily during conversation.

If the ,called party desires to signal the attend-ant he may do so by depress-ing the hooksw-itch once, or by taking special dialing action, t-hen waiting for the attendant to answer.Y The recall logic 1390 will set the recall hip- Yflop Rf. With flip-hop Rf in the set 1 state, the busy 'lamp gate 1363 is inhibited by the 120 IPM interrupter output at gate 1361. Even when the loop is again closed by the subscriber, flip-flop Rf remains set and the lamp '-1360 continues to'flash,

The yattendant .answers a hashing recall by operating the answer key 1370 to its answer position. An off normal spring on the answer key resets flip-flop Rf and the busy lamp again burns steadily. It the trunk party desires to talk to another local party, the attendant depresses a common trunk release key 1325 which resets the electronic trunk circuit to normal and releases the connection to the local subscriber. The diall lamp 1320 will burn as before and a new number may be dialed.

At disconnect, the release of the local trunk is under the control of the attendant. -When the local loop is opened at disconnect, the busy lamp will ash as mentioned for flashing recall.V When the atten-dant answers, the busy vlamp will extinguish. ToV release the trunk, the attendant operates the common trunk release key 1325 thus clearing the electronic trunk and resetting ip-op Et. The trunkrloop is opened and the trunk circuit released.

For outgoing callsthe operation is essentially the same as described in said copending application. A connection is estab-lished between the calling local subscriber and the trunk circuit, which by means of the l-oop closure logic 350 .causes the flipdlop Et to be set. This causes the loop to the central office to be closed through loop closure switch 1330,y the busy Ilamp 1360 to burn, and the train of pulses to be returned in time slot DP29 by Way of gate 336 lto the common supervisory conductor E2. The busy conductor C1 also has a train of pulses in time slot DP29 fnom :gate 334. The flip-flop Et follows dial impulses from the local subscriber, causing the impulses to be repeated to the central oce by means ofthe loop closure switch 1330. To provide the flashing recall feature, the common control equipment described in said prior copending applic-ation needs some modification. For Vexample referring to FIG. 6 of said prior application, an .additional recirculatsnor/,aso

ing dip-flop designated Kb may be added, .and a corresponding column of cores in the low speed memory lll@ having cores only in the trunk rowsl This ilip-lop may .'be controlled by logic in the trunk and transfer logic unit 661. Also the output Xl@ from the trunk transfer sequence logic unit 6&2 is used. The recall is initiated by the local subscriber .by depressing the hookswitch once or by dialing `a digit greater than one. Reference should be made lto section .ld 4of said prior copending application for a description of the transfer action. Making use of the logic quantities described in the prior application, the following equations should be added to Iaccomplish the hashing recall transfer. In response to the loca-l subscriber depressing the hookswitch or dialing a digit greater than one, the transfer sequence switch is advanced to its state X16.

This causes the recirculating flip-flop Kb, `and the lashing recall hiphop Rf' of the particular trunk to be set.

K=R=XPZXT The transfer sequence switch is then set to the clear state. XSL-XllJ/Yt The transfer then proceeds .as described in section Mb of said prior application.

While I have described above the principles of my invention in connection with specific apparatus it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope ot" my invention.

What is claimed is:

In a communication switching system in which a loc-al exchange serves a plurality of local subscriber lines and a plurality of trunk lines extending to a central eX- change, ywith switching equipment in the local exchange tor selectively establishing connections between any two local line terminals or between a local line terminal and trunk line terminal;

said switching equipment comprising common control apparatus which includes a source of cyclically recurring pulses in individual time slots, and la recirculating memory arranged to store switching information associated with the individual time slots and during each time slot to supply tne information to and receive signals from associated circuits and to selectively modify the information, with each of said trunk lines being individually lassociated with `one of said time slots;

trunk circuits individually associated with the trunk lines for controlling connections to the corresponding terminals, each trunk circuit comprising an answer key means hav-ing a normal condition and an answer condition,

supervisory gate means having an input connection to a line from said pulse source on which cyclically recurring pulses appear in the time slot individually associated with the corresponding trunk ine and having an output connection to a common time division multiplex supervisory conductor for supplying supervisory signals to said switching equipment,

and ringing detection means coupled to the associated ytrunk line, including a bistable device, arranged to set said device to an oil-normal state in response to the beginning of a ringing current signal received over the trunk line;

means responsive to the oil-normal state of the ringing detection bistable device for indicating the call and for enabling the supervisory gate means to couple Said cyclically recurring pulses in the individual time `sl-ot of the trunk line to said common supervisory conductor to cause an inuse condition of the trunk to be registered by said switching equipment,

means responsive to actuation of the answer key means one extreme.

to the .answer condition for resetting the ringing-detection bistable device to normal while maintaining the supervisory gate means enabled to supply said fcyclically recurring pulses to the common supervisory `conducto-r to continue the in-use registration in the switchin equipment.

2. ln -a communication switching system, the combination as claimed in claim l, wherein said ringing detection bistable device remains set to its oit-normal state until the answer hey means is actuated to the 4answer condition, irrespective of whether or not the ringing current continues :to be received on `the trunk line.

3. In a .communication switching system, the combination -a-s claimed in claim l, further including an operators calling device and signalling circuit,

each said trunk circuit including dial-control key means,

and an arrangement for coupling said comm-on calling device and signalling circuit to said supervisory signal means of the trunk circuit having its answer key means in the answer condition and its dial control key means in a normal condition, so that signals generated by said calling device enable said supervisory .gate means to supply said cyclicaflly recurring pulses in said individual time slot by way of said common conductor to 'the switching equipment to cause a connection to ybe established between the trunk line terminal and a local line terminal.

f. ln 'a communication switching system, the combination as claimed in claim 3, wherein each sai-d trunk circuit includes a busy lamp which is caused to be light-ed whenever `the trunk circuit is in use, and a recall bistable device,

means responsive to a recall signal from the connected local line terminal for setting the recall bistable device to .an oil-normal condition, to thereby couple an interruptor signal to .said busy lamp to cause it t-o dash, :the recall bistable device remaining set and therefore the busy lamp continuing .to iiash .independently of the yrecall signal from the local line terminal,

means responsive to the actuation of the answer key means to fthe answer condition for resetting the recall bistable device,

S. In a communication switching system, the combination as claimed 'm claim ffl, wherein .said dialing control key means is so larranged that with the answer key means in the answer condition and the dialing control ked means 4in the normal condition the common cal-ling device and signalling circuit is coupled to the supervisory gate means of the corresponding trunk cir-cuit to supply cyclically re curr-ing pulses to the common conductor, and with the answer key means in the yanswer condition and the dialing control means in Van off-normal condition, the cornmon calling device land signalling circuit is associated with said ltrunk line so that calling signals may be transmitted over said trunk line to said central exchange,

the 'arrangement `being such that the common calling device and signalling circuit is never associ-ated with `both the supervisory gate means and the trunk line 'at the same time.

I d, in a communication switching system, the `corr-l tion as claimed in claim 5, further including a comme release key means,

an arrangement coupling the recurring pulses of any trunk circuit having its answer key means in the answer condition `to the common release key,

and means responsive to the actuation of the release key means for causing a release signal to be .transmitted to the switching equipment to thereby cause the rele-ase ot' the connection between a local line terminal and the terminal of said trunk circuit.

'7. ln la communication switching system, the combination `as claimed in claim 5, wherein said answer key means comprises a switch having three positions, non mal, answer and hold and the normal position is f 3,197,569 M 7 s 8. In a communica-tion switching system, the combinaenabling said `supervisory gate means to supply said tion as claimed in claim l, in which an in-use registration 'l cyclically recurring pulses in the individual time slot in the'switching equipment for Ieach said trunk line ter- Vto said common conducto-r,

minal may be effected responsive Ito said cyclically re- A and means also responsive to said bistable devicebecurring pulses in the individual time slot of that trunk 5 Y ing in the set condition for closing a connect-ion belne lon said' common conductoryor for yan outgoing call tween said trunk line and said switching equipment.

in response to seizure of the trunk line for a connection Y R f C't d h th E from a calling loc-a1 llne; e elens l e y e Kammer t lwherein each said trunk circuit'further includes `a loop- UNITED STATES PATENTS v vcontrol bistable device .and means for operating it 10 2,827,517 V3/58 Armstrong 179-27 under the control of said common control apparatus 2,993,095 7,/61 Arnold 179-27 to be in Aa `set Icondition whenever there is an infuse Y3,055,982. Y 9/'62Y Kowalik 179-27 registration corresponding to that trunk line in said Y Y t conrnon control apparatus, land means responsive t0 ROBERT H' ROSE Pnmary Examiner' this bistable device being in the set condition for 15 WALTER L. LYNDE, Examiner. 

1. IN A COMMUNICATION SWITCHING SYSTEM IN WHICH A LOCAL EXCHANGE SERVES A PLURALITY OF LOCAL SUBSCRIBER LINES AND A PLURALITY OF TRUNK LINES EXTENDING TO A CENTRAL EXCHANGE, WITH SWITCHING EQUIPMENT IN THE LOCAL EXCHANGE FOR SELECTIVELY ESTABLISHING CONNECTIONS BETWEEN ANY TWO LOCAL LINE TERMINALS OR BETWEEN A LOCAL LINE TERMINAL AND A TRUNK LINE TERMINAL; SAID SWTCHING EQUIPMENT COMPRISING COMMON CONTROL APPARATUS WHICH INCLUDES A SOURCE OF CYCLICALL RECURRING PULSED IN INDIVIDUAL TIMR SLOTS, AND A RECIRCULATING MEMORY ARRANGED TO STORE SWITCHING INFORMATION ASSOCIATED WITH THE INDIVIDUAL TIME SLOTS AND DURING EACH TIME SLOT TO SUPPLY THE INFORMATION TO AND RECEIVE SIGNALS FROM ASSOCIATED CIRCUITS AND TO SELECTIVELY MODIFY THE INFORMATION, WITH EACH OF SAID TRUNK LINES BEING INDIVIDUALLY ASSOCIATED WITH ONE OF SAID TIME SLOTS; TRUNK CIRCUITS INDIVIDUALLY ASSOCIATED WITH THE TRUNK LINES FOR CONTROLLING CONNECTIONS TO THE CORRESPONDING TERMINALS, EACH TRUNK CIRCUIT COMPRISING AN ANSER KEY MEANS HAVING A NORMAL CONDITION AND AN ANSWER CONDITION, SUPERVISORY GATE HAVING AN INPUT CONNECTION TO A LINE FROM SAID PULSE SOURCE ON WHICH CYCLICALLY RECURRING PULSES APPEAR IN THE TIME SLOT INDIVIDUALLY ASSOCIATED WITH THE CORRESPONDING TRUNK LINE AND HAVING AN OUTPUT CONNECTION TO A COMMON TIME DIVISION MULTIPLEX SUPERVISORY CONDUCTOR FOR SUPPLYITN SUPERVISORY SIGNALS TO SAID SWITCHING EQUIPMENT, AND RINGING DETECTION MEANS COUPLED TO THE ASSOCIATED TRUNK LINE, INCLUDING A BISTABLE DEVICE, ARRANGED TO SET SAID DEVICE TO AN OFF-NORMAL STATE IN RESPONSE TO THE BEGINNING OF A RINGING CURRENT SIGNAL RECIEVED OVER THE TRUNK LINE; MEANS RESPONSIVE TO THE OFF-NORML STATE OF THE RINGINGDETECTION BISTABLE DEVICE FOR INDICATING TO CALL AND FOR ENABLING THE SUPERVISORY GATE MEANS TO COUPLE SAID CYCILICALLY RECURRING PULSES IN THE INDIVIDUAL TIME SLOT OF THE TRUNK LINE TO SAID COMMON SUPERVISORY CONDUCTOR TO CAUSE AN IN-USE CONDITION OF THE TRUNK TO BE REGISTERED BY SAID SWITCHING EQUIPMENT, MEANS RESPONSIVE TO ACUTATION OF THE ANSWER KEY MEANS TO THE ANSWER CONDITION FOR RESETTING THE RINGING-DETECTION BISTABLE DEVICE TO NORMAL WHILE MAINTAINING THE SUPERVISORY GATE MEANS ENABLED TO SUPPLY SAID CYCLICALLY RECURRING PULSES TO THE COMMON SUPERVISORY CONDUCTOR TO CONTINUE THE IN-USE REGESTRATION IN THE SWITCHING EQUIPMENT. 